Hi i need a bit of advice we have a 10 year old cat barney who has always been on is own with us ,recently (about 3 months) wee have ended up with another cat cus he was homless and he is about 1 an a half called marley,once marley came all he wanted to do was play with barney so there was alot of hissing but no physical fighting but recently marley is cornering barney an standing over him an now fighting can someone help please.